package foundation.动态规划.一维动态规划;

/**
 * @author hang an
 * @since 2025/7/16
 */
public class R509斐波那契数 {
    public int fib(int n) {
        return f2(n);
    }

    private int f1(int n) {
        if (n <= 1) return n;
        return f1(n - 1) + f1(n - 2);
    }

    private int f2(int n) {
        if (n <= 1) return n;
        int[] dp = new int[n + 1];
        dp[0] = 0;
        dp[1] = 1;
        for (int i = 2; i <= n; i++) {
            dp[i] = dp[i - 1] + dp[i - 2];
        }
        return dp[n];
    }
}
